This invention relates to air-suspension systems used on vehicles such as automobiles and more particularly to devices designed to compensate the operating characteristics of the air springs in such automotive suspension system.
In general, an air spring inherently has a spring rate which increases with increase in amount of the load applied thereto, as illustrated in FIG. 3 of the accompanying drawings by the line a. Such spring characteristic is advantageous in that it makes it possible to support high loads smoothly without impairing riding comfort of the vehicle but is disadvantageous, incurring different undesirable phenomena which reduce the driving stability of the vehicle. Specifically, in the lower load region, the spring rate is extremely reduced to increase the rate of change in spring stroke relative to change in load. Because of this, for example, when the vehicle is suddenly braked and the loads on the rear wheels are accordingly rapidly reduced, the air springs associated with the rear wheels are allowed to expand to such a large extent that the phenomenon of "tail lift", that is, the floating up of the rear portion of the vehicle body, occurs in a conspicuous fashion. Also, during turning movement of the vehicle, as the loads on the inside and outside wheels are, respectively, decreased and increased under the effect of the centrifugal force acting on the vehicle, the air springs associated with the inside wheels are allowed to expand in an amount larger than that in which the air springs associated with the outside wheels are compressed and thus the rolling movement of the vehicle body is intensified.